In recent years, attempts have been made to carry out target detection utilizing a sensor including, instead of antibodies that bind specifically to a target, binding nucleic acid molecules (a so-called “aptamers”) that bind specifically to the target. As such a sensor, there has been reported a sensor configured so that DNA having an ability to catalyze a redox reaction (referred to as “DNAzyme” hereinafter) is linked to binding nucleic acid molecules in order to examine the binding of a target to the binding nucleic acid molecules (Non-Patent Document 1), for example. In this sensor, self-association of the binding nucleic acid molecules and the DNAzyme occurs in the absence of the target, whereby the catalytic ability of the DNAzyme is inhibited (OFF). On the other hand, in the presence of the target, the self-association is released by the contact of the target with the aptamers, whereby the catalytic ability of the DNAzyme is activated (ON). Thus, if the target is present, the DNAzyme with its catalytic ability being activated causes a redox reaction, so that the target can be analyzed indirectly by measuring the reaction.
However, the above-described sensor requires ON-OFF control of the catalytic ability of the DNAzyme used in the sensor, depending on the presence or absence of the target. Also, in order to further improve the analytical sensitivity in the analysis using the sensor, it is necessary to use a DNAzyme exhibiting a stronger catalytic ability, for example.
ELAA (Enzyme-linked Aptamer Assay) using binding nucleic acid molecules (aptamers) is a method using binding nucleic acid molecules labeled with biotin, for example. In this method, an enzyme, such as horseradish peroxidase or alkaline phosphatase, fused with streptavidin is bound to the biotin-labeled nucleic acid molecules, and binding of a target to the binding nucleic acid molecules is analyzed by detecting the substrate for the enzyme. However, in ELAA, labeling of the binding nucleic acid molecules is essential, and in order to further improve the analytical sensitivity, it is necessary to improve various condition settings, for example.
As described above, in the case where the above-described sensor is used, it is necessary to make various improvements in order to perform more reliable analysis.
Under these circumstances, there are demands for a method that can detect a target easily using binding nucleic acid molecules and also can improve the analytical sensitivity easily.